Background. Children up to the age of 5 years affected by HIV are the most vulnerable subgroup of HIV populations globally, especially in low-resource areas. This is because of the strategic, volatile, and vulnerable nature of this highly sensitive period of child development. Mediational intervention for sensitizing caregivers (MISC) has a structured training program to enable caregivers to improve their children's cognitive and social development during everyday casual interactions in the home. In our preliminary NIMH R34 findings, Ugandan HIV children of caregivers receiving MISC training biweekly for a year showed significantly greater gains on the Mullen Early Learning Scales Composite of g fluid intelligence, when compared to children whose caregivers received a standard health/nutrition education intervention (treatment as usual or TAU). The MISC caregivers were also significantly less depressed, and their child mortality that year was significantly lower. Intervention Method. One hundred Ugandan HIV-positive preschool and 200 HIV orphan caregiver/child dyads will be enlisted from Kayunga and Pallisa Districts. These dyads will be randomly assigned by village clusters to either biweekly MISC or health/nutrition education TAU intervention for one year. Child Outcomes are the child development gains on the Mullen, the Early Childhood Vigilance Test (ECVT) of attention, and the Color- Object Association Test (COAT) of memory, the Behavior Rating Inventory of Executive Functioning - Preschool (BRIEF-P), and the caregiver administered version of the Achenbach CBCL. Caregiver Outcomes include an array of emotional wellbeing (EWB) and daily functioning measures validated during the initial qualitative study phase. Study Aim 1 will evaluate if MISC significantly enhances child outcomes when compared to controls for both HIV-positive and orphan children when assessed from baseline to 6, 12, and 18 months. Study Aim 2 will evaluate if MISC significantly enhances caregiver EWB and daily functioning outcomes. To better understand the mechanisms of MISC-enhanced child development, a Secondary Aim is to evaluate the mediating effect of improved caregiver EWB outcomes on corresponding child development gains, and the modifying effects of caregiver HIV illness and functioning on child outcomes. The Overall Impact comes from establishing the feasibility, acceptability, and effectiveness of MISC for HIV orphans and vulnerable children (OVC) and their caregivers in low resource settings;the sustainability of MISC in low resource settings since it is not dependent on published materials or outside resources;the complementary dual impact of significant psychotherapeutic benefit for the caregiver, especially mothers struggling with HIV disease. MISC will also reduce HIV child mortality because in our initial R34 findings, MISC heightened maternal bonding, sensitivity to serious illness, and the prompter seeking of medical care. It also can improve treatment adherence. Finally, our evidence-based MISC caregiver training interventions can be readily implemented globally as a sustainable way to augment OVC cognitive, psychosocial, and medical wellbeing. PUBLIC HEALTH RELEVANCE: Early childhood (up to age 5 yrs) is a period of dramatic change in the cognitive, emotional, social, and behavioral domains;children continuously progress by observing and interacting with the world around them. In the face of economic instability and nutritional, medical and educational deprivation, HIV-affected very young children are the most vulnerable HIV subgroup globally because their families are often the most vulnerable, with little margin for sustaining a favorable developmental milieu for the child. Through strategic caregiver interventions during this sensitive period of child neurodevelopment, our study findings have the potential for positively re-directing the developmental trajectories of tens of millions of HIV-affected children globally.